Our long-range goal is to characterize active ion transport by the isolated lepidopteran midgut and to define its role in epithelial function during development. We are using proven cytological, biophysical, and biochemical techniques to describe, characterize, and isolate the components of the transport mechanism and plan to reconstitute it in the form of liposomes and planar lipid bilayer membranes from these component parts. Our specific aims are (1) to describe the morphology and fine structure of the midgut (2) to study the biophysics of the three midgut regions (3) to determine the reasons for loss of transport capacity in vitro and to prevent it (4) to analyse the effects of Bacillus thuringiensis toxin as a K-pump inhibitor (5) to analyse cellular ion concentrations with an electron microprobe and (6) to isolate and purify the apical plasma membrane of goblet cells, to isolate portasomes, to isolate the K-modulated ATPase and other transport molecules and to reconstitute the system from its isolated components.